Asteroids; Remote But Real Threat to Earth

A space rock big enough to cause widespread damage and death will hit the Earth only about once every 1,000 years, but experts say the destruction would be so extreme that nations should develop a joint defense against asteroids.

Participants at a NASA-sponsored conference on the hazards of comets and asteroids smashing into Earth that took place in early September in Washington, estimated that the planet probably would be hit about once each millennium by a space rock big enough to release about 10 megatons of explosive energy.

Such a rock, estimated at 60 meters across, scorched through the atmosphere over Tunguska in Siberia in 1908 and flattened trees across 2,000 square kilometers of forest land. No crater was found and experts believe the damage came from atmospheric shock.

Bigger space rocks, which would cause considerably more damage, would hit the Earth even more rarely.

An object of about 1,000 feet "would flatten everything in an area the size of New Jersey (U.S.A.) and kill everybody there," said one of the experts of the University of California, Santa Cruz. The planetwide effects of such a catastrophe are unknown, he said, but debris thrown into the atmosphere could diminish sunlight and perhaps affect agriculture for months.

If such a rock should hit the ocean, it could trigger tsunamis, giant waves hundreds of feet high, to roll through and destroy coastal cities.

A planet-killer asteroid, big enough to destroy whole species, would be rarest of all. The last came 65 million years ago when a six-mile-wide rock wiped out the dinosaurs and about 70 percent of all species.

It is believed that most asteroids that pose catastrophic danger would be spotted decades before they could endanger Earth. This makes it theoretically possible to deflect the speeding space rock and send it into a new, safer direction.

However, unlike Hollywood films that have had crews blowing up such asteroids, the most promising method of deflection would be to change the path of the asteroid slowly, over decades, using small rockets or other devices, Asphaug and other experts believe. Some have suggested that solar concentrators placed precisely on an asteroid could heat and vaporize enough rocky material to provide a thrust that would reshape the object's orbit to spare Earth.

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Khorsheed.com - Sep 2002